Signal telephone system



July 16, 1935,

w. H. WAITE SIGNAL TELEPHONE SYSTEM Filed April' 1, 1933 2 Shets-Sheet 1INVENTQR AX W July 16, 1935. 0 w, w E 2,007,990

S IGNAL TELEPHONE SYSTEM Fild April '1, 1953 2 Sheets-Sheet 2 3 [A /0' V56 a 8? Em I Q \IMI 67 g 6 60 6 20 6f 92 INVENTOR 'ATTORNEYS Palm-.1July 1c, 1935 I .JNITED STATES PATENT OFFICE This invention relates to asignal telephone system especially adapted for use in hospitals,

although the invention 'is not limited to this use. A telephone systemof this type is disclosed in 5 my prior Patent No. 1,841,771, datedJanuary 19,

rality of substations connected to the master station and located in thevarious patients private rooms, adjacent the beds of patients in wards,or the like, and corresponding signal devices, such as lights or audiblesignals are located at the master station corresponding to the severalsubstations, over or adjacent to the doors of the patients privaterooms, over or adjacent the beds or the patients in the wards, on theirinstruments, or the like, and pilot signals, preferably visual, arelocated at the heads of corridors, over the doors" of the wards, or thelike, to indicate that a patient in that particular corridor or in thatparticular ward is signaling. The improvement of the present inventionresides principally in the arrangement of the circuits whereby theamount of necessary wiring is. reduced to such a degree that theexisting annunciator wiring in a hospital may be used withoutsubstantial change, and the former annunciator system converted into atelephonic system. For example, in the system of the aforementionedpatent there are two individual wires for each substation and threecommon wires, whereas in the new system of the presentinvention thereisonly oneindividual wire for each substation and tour common wires.Accordingly, in a typical installation having twenty substations, thesystem of the patent requires 43 wires and the new system of thisinvention requires only '24 wires, or approximately of the total wiring,which considerably reduces the cost and size of the maincables,'simplifics the installation of the system in new and existinghospitals, and permits the use of existing annunciator cable withoutsubstantial change in so far as the number of wires is concerned. a v

In the preferred embodiment of the invention, actuation of a substationsignal button by a patient energizes a corresponding signal at themaster station in the nurses or central oflice and the pilot and doorsignals, and prepares the talking circuit for establishment by the nurseresponding at the master station. In responding to the signal, the nurseactuates a corresponding key, switch, or the equivalent, whichdeenergizes the master station and pilot signals and establishes thetelephonic circuits between the nurse's and the patientstelephone-instruments and the circuit is ready for communication betweenthe nurse-and the patient in response to the patients original signal.Restoration of the nurse's switch opens the talking circuit, but thesignals are maintained until the patients button is released, which islocked in closed position after manipulation, so that the signals remainuntil responded to. An auxiliary audible signal is also preferablyprovided at the master station to call attention to a calling patient,but the signal does not remain energized when the button is lockedclosed, althoughit is energized each time the patient presses the lockedbutton.

In a modified arrangementsof the system of the present invention, thenurse at the master station, by throwing a switch, completes her talkingcircuit from her transmitter to the patients loud speaker, so that thenurse may talk to the patient at any time and the patient mayrespondu,

by pressing the corresponding button to complete the patients talkingcircuit between the patients transmitter and the nurse's receiver. Thispaging feature is a. valuable adjunct in a hospital signaling system,for the reason that with it a supervisor may communicate with any andall of the patients in a short time without making many personal tripsto the patients private rooms or to the 'wards in accordance with theusual practice.

It will be seen that the present invention has all of the advantages offacilitated communication between the several patients and the nurse, I

which are incorporated in the system of the aforementioned patent, andhas the additional advantages of simpler wiring, the paging feature,

and other advantages which will be ascertained upon reference to theaccompanying drawings,

Referring to Figure 1 of these drawings, letters A. B. C, D, E and Fdesignate the substations in the various patients private rooms in ahospital, or the several beds in a ward which is equipped with thesubstations mentioned. The letter M designates the master station in thenurses office to which the several substations are connected.

- The master station M in the nurses" office is equipped with aplurality of switches, keys, or the like, designated a, b, c, d, e and1, corresponding to thesubstations A, B, C, D, E and F, respectively,The master station M is also equipped with the visual signals al, bl,cl,- dl, el, and fl, individual to the keys a, b, c, d, e and f, andcorresponding to the substations A, B, C, D, E and F, respectively.These visual signals may be shutters or flags, as indicated, signallights, or the equivalent, and are so arranged that when a flag israised or a light illuminated it identifies visually the substationwhich is calling.

Each of the substations A, B, C, D, E and F is provided with acorresponding visual signal Al, Bl, Cl, DI, El, and Fl, which arelocated over or adjacent the .doors of the corresponding patientsprivate rooms, over or adjacent the corresponding bed or on theinstrument in the ward, or the like.

Also, located at the head of a corridor, wing, or section of patientsprivate rooms over or adjacent the door of a ward, or the like, is avisual signal in the form of a pilot lamp P, which indicates that apatient in that corridor or wing, section, ward, or the like, issignaling, and a nurse may then identify the particular patient who issignaling by his or her private lamp Al, Bl, Cl, Dl, El, or Fl. Asindicated in Figure 1, one of the pilot lamps PI is individual tosubstations A, C, E, and the other pilotlamp P2 is individual tosubstations B, D, E, which in the particular arrangement illustrated,may be the way in which the private rooms are divided by the corridors,wings, or sections, or the way in which the substations are classifiedor arranged in wards, or the like.

The substations A, B, C, D, E and F are all alike and therefore thedescription of one of them, namely, substation A, will suffice for all.The substation includes a patients receiver Ill, which is preferably aloud speaker, a patients transmitter H, which is preferably amicrophone, and a push button l2, which the patient depresses when hewishes to speak to the nurse at the nurses oflice. be mounted in or on aportable casing standing adjacent the patients bed, or the like, and thepush button may be conveniently placed at the end of a flexible cord soas to be available to the patient. The push button l2 locks in closedposition afterbeing pressed and remains in closed position until it isreleased. Any suitable type of locking button may be employed and forpurposes of illustration a diagrammatic form of locking button isdisclosed. This button includes a first contact II which is providedwith an extension which hooks under the abutment of a latch l4, so thatthe spring contact I3 is held down after the button I2 is pressed. Belowthe first spring contact I8 is a second spring contact l5, adapted to beengaged by first spring contact I 3 and remain eng ged therewith whilelatch i4 holds first contact i 3 in closed position. Similarly, belowsecond spring contact I5 is a third spring contact I, adapted to engagetherewith; below third spring contact I is a fourth spring contact l1,adapted to engage with the former,v and below the fourth The instrumentsenumerated may spring contact I1 is a fifth spring contact ll, adaptedto engage with the former. The fifth spring contact l8, however, doesnot remain engaged with fourth spring contact I! when the first springcontact I3 is held locked in closed position by latch l4, although allof the other spring contacts are in mutual engagement. Fifth springcontact I8 is only engaged with. fourth spring contact l1 when thebutton l2'is depressed below the point at which the latch l4 engages it.Thus,

when the patient presses. button l2 all of the spring contacts,including fifth spring contact it are in engagement, but when thepatient releases pressure on button l2, fourth spring contact ll becomesdisengaged from fifth spring contact. it, although the latch holds thefirst, second, third and fourth spring contacts l3, l5, l6 and I1,respectively, in engagement. The purpose of this arrangement will bedescribed later.

First spring contact I3 is connected by wire I! to a contact 20 normallyengaged with armature 2i of relay 22, and armature 2| is in series withpatients microphone II, which is connected by wire 23 to the talkingwire 24 of the main cable of the system.

The second spring contact I5 is connected by wire 26 to relay22, theother terminal of which is connected by wire 21 to switch contact 28 ofkey a, and this contact is normally engaged with contact 29 connected bywire 30 to the relay 3| of signal flag al, and the other terminal ofthis relay is connected to wire 32, which in turn is connected to thepositive line wire 33 of the main cable, which is connected to-thecorresponding pole of signal battery 34, the negative terminal of whichis connected to negative line wire 35 of the main cable. The patientsloud speaker Ill is connected in parallel with the relay 22 and one ofthe leads of the loud speaker l0 contains the condenser 36, the purposeof which will bedescribed later. The armature 31 of fi relay 3| isadapted to engage spring contact 3 when the-relay 3i is energized toclose a circuit leading from positive line wire 33, wire 32, springcontact 38, armature 3l of flag relay 3i, wires and 4|, pilot lamp Piand negative line wire 35.

The third spring contact l8 of the patients push button switch isconnected by wire 42 to the corresponding door, bed or instrument lampAl,

which is connected by wire 43 to positive line wire 33.

The fourth spring contact I! of the patients push button switch is thenegative feed forthe push button and is connected by wire 44 to negativeline wire 35.

The fifth spring contact l8 of the patients push button switch isconnected by wire 46 to line wire 41, which is the audible signal wireof the main cable and is connected by wire 41' to the audible signal 43at the master station, which may be in the form of a buzzer, or thelike, the other side of which is connected through disconnect switch 49by wire 50 to the positive line wire 33. The use of the buzzer 48depends upon requirements, and it may be omitted if not required andthus one of the line wires of the main cable will be eliminated, namely,wire 41.

Each of the other substations B, C, D, E and F, is provided with anindividual wire 21 corresponding to wire 21 to substation A, this wirebeing connected to the corresponding key at the master station, and theother wires 23', 44' and 46 leading from the remaining substations, B,

C, D, E and F, correspond to wires 23, "and" of the substation A justdescribed.

Spring contact 5| cooperating with common contact 28 of nurses stationkey a, which is normally disengaged from common contact 28, is connectedby wire 52 to the nurses transmitter 53, the other pole of which isconnected by wire 54 to spring contact 55, adapted to engage contact 56,which is connected by wire 51 to the positive terminal of talkingbattery 58, the negative pole of which is connected to negative linewire 35 of the main cable.

Joined to spring contact 55 of nurses key a by an insulating block 55,so as to move therewith, is a second spring contact 60, which isconnected by wire 6| to wire 24 of the main cable and which is adaptedto engage spring contact 62 which is connected by wire 63 to nursesreceiver 64, the other terminal of which is connected to the positivepole of talking battery 58 through resistance 65. A second resistance 65is connected across the terminals of the nurses receiver 54. A talkingimpedance coil 61 is interposed between negative line wire 35 and nursesmicrophone 53.

The telephonic circuit just described is shown in the simplifiedschematic diagram of Figure 2 in which the winding of relay 22 isrepresented as an impedance across the terminals of the patients loudspeaker Ill. The connections of the switch, telephonic instruments andsignal devices corresponding to other substations are identical to thosedescribed in connection with substation A and therefore they need not befurther described.

In operation, assuming that the patient at substation A presses pushbutton l2 to signal a nurse at the central oflice, several circuits arecompleted,

one of which includes the buzzer 48' in the central omce, this circuitbeing traceable from signal battery 34, by positive line wire 33, wire50, buzzer disconnect switch 49, buzzer 48, wire 47', buzzer line wire41, wire 46, fifth push button spring contact it, fourth push buttonspring contact I'l, wire 44, negative line wire 35 and back to battery34. When theLpatient releases pressure on push button i2 the fourthspring, contact H disengages fifth buzzer spring contact it to denergizethe buzzer 48, but the remaining spring contacts remain mutually engagedbecause latch It holds themin engagement in the manner 11- lustrated inFigure 1. Subsequent pressure by the patient on button l2 reenergizesbuzzer 48 for as long a period of time as thepatient maintains thebutton 12 depressed. If the patient presses the push button l2insistently, the nurse may silence the buzzer by opening the disconnectswitch 49.

Engagement between third and fourth push button contacts I6 and II,respectively, establishes a circuit from negative contact ll, contactl6, wire 42, door lamp AI, and positive line wire 33. The door lamp Alover the door of the private room of the patient ,who signaled isaccordingly illuminated to indicate tothe nurse which patient iscalling, if the nurse happens to be out of her office, it beingunderstood that the lamp AI may be over the bed of a calling patient inthe ward, or the like.

Engagement between second and third contacts l5 and I5, respectively,establishes a circuit from negative contact I! through contact l6,contact l5, wire 25, relay 22, wire 21, closed contacts 28 and 29 of keya at the nurses station M, wire 33, relay 3|, wire 32 and positive linewire 33. Energization of relay 22 breaks the normal circuit of thepatients transmitter or microphone I l by disengaging armature 2| fromcontact 20. Since this action takes place substantially simultaneouslywith the closing of the circuit of the patients transmitter ormicrophone H by manipulation of the patients push button l2, thepatients talking circuit practically remains deenergized.

Energization oi flag relay 3| causes it to attract its'armature 31 andraise flag or shutter at to designate to the nurse at the master stationM that the patient at substation A is signaling. At the same timearmature 3! engages contact 33 to close a circuit from negative linewire 35, pilot light Pl, wire 45, contacts 3! and 38, wire 32, andpositive line wire The illumination of pilot lamp Pl indicates to anurse, if she is not in her office, that a patient in the correspondingcorridor, wing, ward, or section of the hospital is calling and she maythen, by glancing at the door or bed lamps All, Ci, and El, ascertainwhich of the patients is calling, it being the patient at substation Alin this particular instance.

At the master station M the nurse, having been notified by the soundingof buzzer 48 that a pa tient is calling, glances at the master stationinstrument and identifies the patient because of the display of flag orshutter at. She then manipulates the key a, which breaks the normalconnection between contacts 28 and 29 and makes contact between contacts23 and 5!, 55 and 5t, and 63 and 52. The disengagement of contacts 26and 29 deenergizes flag relay 3i so that flag a drops to break thecontact between armature 31 and contact 33 and extinguish pilot lamp Pi.The disengagement of contacts 28 and 29 also deenergizes relay 22, whichaccordingly releases its armature it so that the latter reengagescontact 20 to remake the circuit of patients transmitter or microphoneH, which is traceable from negative contact ll, contacts it, I and I3,wire l9, contacts 25 and 2 l transmitter or microphone H, wire 23, linewire 25, wire ti, contacts 65 and 52 of key a, wire 53, nurses masterstation receiver 5d, resistance 65, wire 5? to talking battery 58, thusestablishing the patients talking circuit.

Engagement between contacts 55 and 55 and of contacts 28 and 5i of key aestablishes two circuits, one traceable from talking battery 55 throughwire 51, .contacts 56 and 55, wire 55, transmitter 53, wire 52,impedance 6i, line wire 35 back to' talking battery 58 and a circuit inshunt with impedance 5! traceable through wire 52, contacts 5! and 28,wire 23, loudspeaker l3 and blocking condenser 36 shunted by relay 2?,wire 25 contacts l5, l5, l1, wire 45, line wire 35. Although relay 22 isnow in the energized circuit of talking battery 58 the voltage appliedto relay 22 is insuflicient to operate it so that armature 2| andcontact 20 remain in engagement. The patients listening circuit isaccordingly established and communication between the patient and thenurse at the master station may As indicated in the schematic diagram ofFig denser I0 servesto shunt, current from signal battery 34 throughpatients relay 22 when the patients pushbutton I2 is pressed, thusenergizing relay 22. The patients relay22 renders the system selective,for it this. relay were not preseat, all microphones of the otherpatients substations whose pushbuttons were operated would be connectedto the nurse's receiver, so that the latter could hear any noises in therooms of the other patients. Upon completion of the conversation betweenthe patient and the nurse, the latter restores key a to its initialposition. which disconnects the circuits to the nurse's transmitter 52and receiver 54 and, by the reclosure of contacts 28 and 29, patientsrelay 22 and flag relay ii are reenergized separating armature 2i fromcontact 20 on patients relay 22 and reenergizing pilot lamp Pl throughthe closing of contacts 21 and 28 on flag relay 3i, unless the patienthas reopened the locking button in the meantime by releasing the latchi4, whereupon all circuits are reopened including the circuit of relay22, which accordingly releases armature 2| to reengage contact 20 andprepare the normal circuit through patients transmitter or microphone IIfor completion by subsequent manipulation of the patients button i2. Thedoor lamp AI and the corresponding pilot lamp Pi are also extinguishedwhen their corresponding contacts l6 and 31-48, respectively, are open.The system is now restored to its original condition for reoperation byany one of the substations in the manner described.

Incorporation of the paging features, whereby the nurse at the masterstation may talk to the patient at any time without awaiting a signalfrom the patient, is simply made by changing the connections of thepatients loud speaker III. Instead of connecting the patients loudspeaker [0 directly in-parallel with the relay 22, as in the arrangementillustrated in Figure 1, it is bridged across wires 21 and 44, asillustrated in Figure 3. With this arrangement the nurse at the masterstation simply throws key a to establish two circuits, one from talkingbattery 52 through wire 51, closed contacts 56 and II, wire N, masterstation transmitter 52, impedance 61', wire 25 back to talking battery58, and the other from impedance 61 through wire 52, key contacts II and22, wires 21 and I0, patients loud speaker ll, blocking condenser 36,and wires Ii, 44 and II, back to they other side of impedance 8! thusestablishing a talking circuit between the nurse's transmitter i2 andthe patients loud speaker M without any previous preparation of thecircuit by the patient or the display of signals.

Manipulation of the nurse's key also prepares the patients talkingcircuit to the nurse's receiver 84 from talking battery ll, resistance8!, receiver M, wire 63, key contacts 62 and 60, wires I, 24 and 22,patients microphone ll, closed contacts 2| and 20, wire i9, and opencontacts is, ii, I and II. This circuit, 1. e., the patients talkingcircuit, may be completed by the patient upon manipulation of his buttoni2 in the manner described.

Manipulation of the patients button l2 does not, in this instance. breakthe circuit to the patients microphone ll because relay 22 remainsdeenergized.. due to the disconnection between key contacts 20 and 2.resulting from manipul s' tion of the nurse's key. a.

In this waya nurse at the master station may page all of the patientswithout making it necessary for the nurse tomake personal trips to thevarious patients rooms. This is a valuable ad'- junct to a hospitalcommunication system. since in many instances it is desirable for thenurse to locate a doctor or to communicate with the patient withoutleaving the nurse's station.

accordance with the present invention without disturbing the annunciatorcables in any way except to make connections at the open ends thereof.This arrangement is illustrated diagrammatically in Figure 4, in whichthe original annunciator i2 iltted with signals such as lamps A2, B2,C2, D2, E2 and F2,-corresponding to the patients rooms, beds, or thelike, A, B, C, D, E and F, respectively, is employed instead of the flagsignals al at the master station. These lamps or other signals areconnected in the circuits of the nurses corresponding keys to take theplace of the flags al, illustrated in the arrangement of Figure 1. Forexample, the contact 2! of each of the nurse's keys a, b, c, d, e and Iis connected to the corresponding lamp or other signal of theannunciator 12, the remaining connections of the circuit being the sameas illustrated in Figure l and may include the buzzer 48, although thisaudible signal is not shown in Figure 4.

With this arrangement, manipulation of the patientsbutton l2 atsubstation A, for example, closes a circuit from positive line wire 32to the annunciator 12 through wire 12, annunciator lamp or other signalA2, wire 30', normally engaged contacts 29 and 28 of master station keyswitch a, wire 21, substation relay 22 and patients loud speaker I0,wire 28, patients button second contact i5, third contact l8, fourthcontact I'l, wire 44 and negative line wire 3!. The resultantenergization of annunciator signal A2 identifies the calling patient atsubstation A, and the nurse responds as before, by manipulatingcorresponding key a at the master station.

It will be seen that annunciator wire's take the place of'line wires 24,22 and I1 and the individual substation wires 21, and since, theannunciator wires are already installed in existing cables of thehospital, rewiring of the hospital becomes unnecessary, and theattendant labor, noise, and excavation of the walls or floors of thehospital to lay the line wires or cables are eliminated.

It will be seen that the new telephone signal system of this invention,although extremely simple and employing a minimum number of wires andother parts, is nevertheless absolutely selective, wherebycommunications between the master station and the individual patientsremain private. with the paging feature the nurse at the master stationmay throw the key corresponding to the patient to whom she wishes tospeak and talk to the patient at any time and the patient may answer bypressing the button l2 and talking.

While the system of the present invention has been illustrated anddescribed as being particularly adapted for use in hospitals. it is tobe understood that its utility is not limited to this purpose, but thesystem may be employed wherever an intercommunicating telephone systemof simple construction is desired. .Also, while a preferred embodimentof the invention has been illustrated, it is also to be understood thatthe invention is not limited thereby, but is susceptible to changes ofform and detail within the scope of the claims.

I claim:

1. In atelephone system, the combination of a master station'having atelephone instrument, a plurality of substations each having a telephoneinstrument, a plurality of common conductors each connected to saidsubstation and to the master station, and only one wire between eachsubstation instrument and the master station instrument which'isindividual only to those instruments.

2. In a telephone system, the combination of a master station having atelephone instrument, a plurality of substations each having a telephoneinstrument, a plurality of common conductors each connected to eachsubstation and to the master station, only' one wire between eachsubstation instrument and the master station instrument which isindividual only to those instruments, and a switch in each single wirefor connecting and disconnecting the corresponding substation instrumentwith the master station instrument.

3. In a telephone system, the combination of a master station having atelephone instrument, a plurality of substations each having a telephoneinstrument, apluralityof common conductors each connected to eachsubstation and to the master station, only one wire between eachsubstation instrument and the master station instrument which isindividual only to those instruments, and a switch at the master stationcorresponding to each substation and connected in the single wirethereof for connecting and disconnecting the corresponding substationinstrument with the master station instrument.

. f1. In a telephone system, the combination of a master station havinga telephone instrument, a plurality of substations each having atelephone instrument, a plurality of common conductors each connected toeach substation and tothe master station, only one wire between eachsubstation instrument and the master station in-- strument which isindividual only to those instruments, and a switch at each substationcon-- nectedin the single wire thereof for connecting and disconnectingthe corresponding substation instrument with the master stationinstrument.

5. In a. telephone system, the combination of a master station having-atelephone instrument a plurality of substations each having a telephoneinstrument, a plurality'of common conductors each connected to eachsubstation and to the master station, only one wire, between eachsubstation instrument and the master station instrument which isindividual only to those instruments, a switch at the master stationcorresponding to each substation and connected in the single wirethereof, and a switch at each substation connected in the single wirethereof, the master station and substation switches being adapted toconnect and disconnectthe corresponding substation instruments with themaster station instrument.

6. In a telephone system, master station having a telephone instrument,a plurality of substations each having a telephone instrument; aplurality of common conductors each connected to" each substation and tothe a master station, one wire between each substation instrument andthe master station instrument which is individual only to thoseinstruments, a relay in the single wire of each substation, a. secondtelephone responding relay.

plural "f we: substations each. having a telephme instrument, aplurality OI'OQIBIXIOD conductorsand to the each connected to eachsubstation cone telephone-instrument, and the combination of a Yinstrument at each substation controlled by the corresponding relay, anda, switch in each single wire for operating the cor-.

Vmaster station having atelephone instrument, a

which is individual only to those instruments, 9.

relay in the single wire of each substation; a sec-' ond telephoneinstrument at each substation controlled by the corresponding relay, anda switch at the master station for operating the corresponding relay.

r 8. In a telephone system, the combination of a master station having atelephone instrument, a. plurality of substations each having atelephone instrument, a plurality of common conductors each connected toeach substation and to the master station, one wire between eachsubstation instrument and the master station instrument which isindividual only to those instruments, a relay in the single wire of eachsubstation, a. second telephone instrument at each substation controlledby the corresponding relay, and a switch at each substation ioroperatingthe corresponding relay.

9. In a telephone system, the combination of a master station having atelephone instrument, a plurality of substations each having a telephoneinstrument, a plurality. of common conductors each' connected to eachsubstation and to the master station, one wire between each substationinstrument and the master station instrument which is individual only tothose instruments, a relay in the single wire of each substation, asecond telephone instrument at each substation con- 1 to the masterstation, one wire between each substation instrument and the masterstation instrument which is individual only to those instruments, arelay in the single wire of each substation, a second telephoneinstrument at each substation controlled by' the corresponding relay, aswitch in each single wire for operating the corresponding relay, and asecond telephone instrument at the master station connectible to thesecond instrumeninat a substation upon operation'of the correspondingswitch.

11. In; a telephone system, the combination of a master station having atelephone instrument, a substation having a telephone instrument, anormally closed circuit for at least one of said telephone instruments,a switch at the substation for breaking the normally closed circuit ofsaid a switch at the master station for restoring the circuit of saidone telephone instrument and establishing a talking circuit between themaster and said substation instruments.

12. In a telephone system, the a master station having a telephoneinstrument, a plurality of substations each having a telephoneinstrument, a normally closed circuit for each substation instrument, aswitch for breaking the normally closed circuit of the instrument at oneof the substations, and storing the circuit of the instrument at thesaid one substation and establishing a talking circuit between themasterand said substation instru-- ments. V

'13. In a telephone system, thecombination of a master station havingatelephone instrument, -aplurality of substations combination of asecond switch for reeach. having a tele- 1'6 6 aoo'moo phone instrument,a normally closed circuit for each substation instrument, a switch ateach substation ior breaking the normally closed circuit of thecorresponding telephone instrument,

and a second switch at the master station for restoring the circuit ofthe instrument at the said one substation and establishing a talkingcircuit between the master and said substation instruments.

14. In a telephone system, the combination of a master station havingtelephone instruments, a plurality of substations having telephoneinstruments, a normally closed circuit for each substation instrument, aswitch at each substation for breaking the normal circuit of at leastone of the corresponding substation instruments, and a switch at themaster station for restoring the normal circuit of said one substationinstrument'and establishing a communication circuit between the saidmaster station and substation instrument.

15. In a telephone system, the combination of e a master station havingtelephone instruments,

.a plurality oi substations having telephone instruments, a switch atthe master station tor establishing a communication circuit only betweenthe master station transmitter and a substation receiver, a secondswitch at the master station for preparing a second communicationcircuit between the master station receiver and the transmitter of thesaid substation, and a switch at the said substation for completing thesaid second communication circuit.

17. In a telephone system, the combination of remote stations eachhaving telephone instru ments, a switch at one station for establishinga communication circuit between one of the instruments thereof and thecorresponding instrument at another station, a second switch at said onestation for preparing a. commlmication circuit between the otherinstrument thereof and the corresponding instrument at said otherstation, and a switch at the said other station for completing at willthe said second communication circuit.

18. In a telephone system, the combination of a master station havingtelephone instruments, a plurality of substations each having telephoneinstruments, a switch at each substation for preparing a communicationcircuit to the master station, a switch at the master station forcompleting the said communication circuit to the correspondingsubstation, a second switch at the master station for preparing a secondcommunication circuit to the last-named substatiomand a second switch atthe said last-named substation for completing the secondcommtmicatloncircuit.

wnnmnwarrn.

